Help! Going Dual Exhaust

[KANE]

Because it can't create additional power. An internal combustion engine is an air pump. You make power by injesting (and eventually expelling) the maximum amount of air (and yes, fuel, but fuel is not the difficult part to increase in an engine). Backpressure reduces the mount of fresh air that can be pumped into an engine. It's simple physics, and it's common sense.

I don't think its about creating some "magical" additional power that the woman who throws monkey bones on the psychic friends network talks about.

I don't think the assertion has been about creating additional power- it's been about maximizing available potential.

And no one has stated that anyone needs intense amount of back pressure- but rather a small amount can help some engines overcome other problems. Perhaps you are confusing the scope of the subject. Besides- I don't think any of us will be able to escape a small amount of it since we don't live in academia.

No one is insisting that a large motor would make more power if it had unbelievably small primaries, a huge converter, and then three mufflers.

It's about using what is available and setting it up right for a particular purpose. And if a small amount of back pressure gets an engine where it needs to be for any number of reasons- then it has a purpose.

To be honest- it is really a non-issue. If things are set up to be the best they can in a given situation- then it is fine to have back some amount of back pressure. Unless the exhaust exits right at the head- just about everything will impede the escape of the exhaust gases.

In the case of some other components- such as turbos- they fetter the escape of the gas- but provide other benefits. I don't think the back pressure they create is a bad thing either because they create a different benefit that outweighs the back pressure they create- boost. So again- a blanket, polar statement like- all back pressure is bad, has no purpose, and should be avoided in all instances- isn't exactly true. If it were then all cars would have exhaust that exits it at the head and turbochargers wouldn't be used as folks went to extremes to avoid any back pressure whatsoever.


More importantly- the idea that a DOT & EPA legal, street driven car can achieve 0% back pressure, is unlikely to be had.

 

[Evolution1980]

I'm not trying to be rude here, but you have a serious lack of understanding of how an engine works, not only in the mechanical details, but the gas flow dynamics. Please, for your good, and my sanity, get a textbook on internal combustion engines and do some reading.

Lucky for me, I never claimed nor portend to be an SME ("Subject Matter Expert") . Although there are people of that ilk here and they already chimed in much earlier in the thread.

With regards to your sanity being at stake, public forums may not be the best place for you to hang out... :W
You might consider taking your/our question(?) to a forum for physicists or mechanical engineers and then returning back with answer to educate the rest of us.
Or we could all just drop it and let people do as they will, because they will regardless.

 

[73shark]

Kane's statement re: letting the exhaust exit at the head ports got me to thinking that there must be a reason that funnycars/top fuel dragsters have short pipes albeit very large ones. Maybe scavenging has something to do with it.

 

[84Turbo]

Lucky for me, I never claimed nor portend to be an SME ("Subject Matter Expert") . Although there are people of that ilk here and they already chimed in much earlier in the thread.

With regards to your sanity being at stake, public forums may not be the best place for you to hang out... :W This forum claims to be the ultimate hub for information. I'd hate to think that it's just a slogan, and not actual fact.
You might consider taking your/our question(?) to a forum for physicists or mechanical engineers Why? I've already supplied the answer numerous times. and then returning back with answer to educate the rest of us. I've tried the education goal, but some people are unwilling or unable to learn.
Or we could all just drop it and let people do as they will, because they will regardless.

We are finally in agreement! Some people will do what they want, despite the fact it doesn't make any technical sense.

 

[tracksnblades1]

Kescholtz,
Thanks for the interesting read. How is your choke performing, and what type of choke do you have on your 75? Do your know if the 1/4 hp parasitic loss of the air pump is measured at idle speeds or performance rpms? I am glad your satified with your exhausts.
Without getting to deep in physics or The Thermal Dynamics of Internal Combustion, I agree totally with 84turbo. I believe 84turbo provided adecate informed defense of his postion. I don't want to appear to be condascending or imply that I can explain or enlighten better than any of your other resspondants. I would like to point out and support 84turbo position. I understand that the original and primary purposes of the exhaust sytstem was to attenuate the exhaust sound waves and provide a safe exit for the toxic elements of the exhaust. As I remember my instuctions 25 years ago. First, natually aspirated internal engines rely on atomspheric pressure (14.7 psi absolute @ sea level) to acheived cylinder filling. 84turbo explains this pressure differential, The pistons downward movement (intake stroke) causes a low pressure area and the ambient atmospheric pressure comes rushing in. Camshaft and Intake phazing. Theoriticaly a properly engineered phazing of the camshaft and intake will result of a slight supercharging (compressing) effect to occur before intake valve closing and little or no piston movement. (due to the inertial columning effect of the incoming high velocity intake charge) (It just can't stop instantly at 6 grand.) The cylinder is now full of cool (non-egr) dense charge of the properly atomiized (not vaporized) A/F mixture. Compression. 84turbos resistance to crankshaft movement. During compression, the atomized a/f mixture is vaporized due to the heat of compression. Ignition. Power stroke, as 84turbo explains the combustion process imparting its exponential forces of thermal expansion. As the piston travels towards BDC (dependant on camshaft profiles) First the exhaust valve opens
(BBDC) and vents the high pressure exhaust wave into the properly phazed header and intiates exhaust flow with minimal or no piston movement. Exhaust stroke, low pressure exhaust wave or exhaust compression, the piston evacutes the cylinders as 84 turbo explains the resistance to a 4in bore x 3.48in stroke ehausting its contents in a nano second though a 1.60 valve opened a varing height(under the curve) down a primary tube that has multiple bends. This is the resistance to crank movement 84turbo explains. The socalled fifth cycle or some call the two-stroke cycle. Contraversial. In theory the header can be designed evacuate the cylinder and at the. During this time of exhaust valve closing and during little movement of the piston around TDC the exhaust low pressure wave is still traveling out of the header causing a low pressure area to form near tdc as the intake valve is opening(valve overlap both open) Now, The low pressure area created by the scavenging exhaust gases help initiate flow through the contiually openening intake valve. This effect usally pulls new A/F mixture into the exhaust header(eyes burning in the shop at an idle)(top fuel spitting nitro out of the zoomies on the line). Reversion, Low pressure exhaust wave has since stop travelling down the primary tube and the low pressure exhaust reversion wave is traveling to the exhaust valve and (at the turned rpm) stuffs the A/F mixture back into the combustion chambers (two stroke effect) just as the exhaust valve shuts and piston starts accelerating on its intake stroke and intake valve start flowing well. Margin of error? Yes, the question of torque 84turbo explained it. I offer countless examples in the past. Remember the old gas heavy duty trucks. Ever remember seeing a factory IHC, Gmc, Ford with engines as small as 304, 348,331 wearing a set of 2 inch duals? No. More like 3 inch and mufflers that are 12india. x 38 in long. and were governed at 3300rpms that low rpm torque. Ever see a school bus with a 2 inch exhaust pipe 30 feet long. Simply stated cylinder pressure is torque and Hp. VE determines cylinder pressure. EGR valves were designed to introduce superheated exhaust(inert) gases directly to the intake manifold to vaporized the atomized fuel in the a/f mixture and cause lower charge densities (through expansion) to lower volumetric effiencies to suppress detonation by effectly lowering cylinder pressures (somewhat like lower cr ratio) This is what 84turbo was explaining.
Just think of an 800hp, 350cu in, Gasoline (any btu rating) a/f of 12:1 to your iso 14.7:1.
Think its 85% VE? No.
Diesel fun. Duramax, dodge, power stroke 3.5 to 4.0 inch pie r squared
n14 cummin 5 inch
1150 cummins compounded 6inch
Picture this an open class tractor pull engine compounded turbo only major restiction on engine Turbo inlet size and exhaust outlet size. almost like nascar. Thanks Just for fun.

 

[Evolution1980]

tracksnblades1, Welcome to the

If you haven't done so yet, stop into the New Member Introductions forum and say "Hello!" to everyone!

 

[73shark]

I thought the EGR function was to lower combustion temperature to inhibit the formation of nitrogen oxides.

 

[92BlackVette]

I thought the EGR function was to lower combustion temperature to inhibit the formation of nitrogen oxides.

Exhaust gas recirculation (EGR) systems were introduced in the early '70s to reduce an exhaust emission that was not being cleaned by the other smog controls. Oxides of nitrogen (NOx) are formed when temperatures in the combustion chamber get too hot. At 2500 degrees Fahrenheit or hotter, the nitrogen and oxygen in the combustion chamber can chemically combine to form nitrous oxides, which, when combined with hydrocarbons (HCs) and the presence of sunlight, produces an ugly haze in our skies known commonly as smog. - [SIZE=-1]Henry Guzman 11/5/1997 [/SIZE]

 

[73shark]

At least my memory hasn't completely gone south.

 

[KANE]

Exhaust gas recirculation (EGR) systems were introduced in the early '70s to reduce an exhaust emission that was not being cleaned by the other smog controls. Oxides of nitrogen (NOx) are formed when temperatures in the combustion chamber get too hot. At 2500 degrees Fahrenheit or hotter, the nitrogen and oxygen in the combustion chamber can chemically combine to form nitrous oxides, which, when combined with hydrocarbons (HCs) and the presence of sunlight, produces an ugly haze in our skies known commonly as smog. - [SIZE=-1]Henry Guzman 11/5/1997 [/SIZE]

And... it is a Federally regulated requirement. :eyerole

At least my memory hasn't completely gone south.

I hear ya!

 

[tracksnblades1]

And... it is a Federally regulated requirement. :eyerole







I hear ya!

Yes, I stand corrected. Excellent memory, I believe you are right EGR valves did debut in the early 70's in the automotive industry. I wonder if the were used prior in any othe Federally regulated or nonregulated enities? Additionally I wonder if the aviation industustry realizes the benefits of back pressure in their exhaust systems. I have however never seen to many exhaust system on airplanes. It would be interesting to see if their benefits would out way their weight. Can one imagine the variables incountered in aviation, transportation, and shipping industries has faced in the past and what their findings were.